This disclosure relates generally to processes for the preparation of higher alcohols from ethanol and n-hexanol by Guerbet condensation.
Higher alcohols, having from 8 to 16 carbon atoms, are valuable for use as plasticizers such as cold-resistant auxiliary plasticizers of plastics, antifoaming agents, dispersing agents, surfactants, mineral separation agents and petroleum additives. Higher alcohols are also valuable for use in other applications such as in cosmetics, printing and dyeing, paint, and photographic film.
Lower alcohols, having from 2 to 4 carbon atoms (ethanol and n-butanol), are useful as fuel additives. However, there are problems associated with the use of ethanol fuel in internal combustion engines, including its water solubility, corrosivity and the differences in its fuel properties compared to gasoline. In order to overcome the disadvantages of ethanol as a fuel, catalytic condensation of ethanol to n-butanol can be carried out. Compared to ethanol, n-butanol has several advantages. For instance, n-butanol can be burned in the existing gasoline engines without practically any engine or car modifications and it has higher energy content and air-to-fuel ratio.
n-butanol can be obtained by means of the well-known Guerbet reaction, which makes it possible to catalytically convert ethanol to n-butanol. Preparation of n-butanol by Guerbet synthesis from ethanol problematically results in the production of significant amounts n-hexanol. Typically from about 0.05 to about 0.1 moles of n-hexanol are generated in Guerbet condensation of ethanol per mole of n-butanol produced. Problematically, as compared to ethanol and butanol and as further compared to higher alcohols having from 8 to 16 carbon atoms, n-hexanol has limited industrial applicability, is of lower value, and is typically incinerated for energy recovery.
A need therefore exists for improved processes for the generation of higher alcohols by Guerbet condensation of lower alcohols wherein the amount of n-butanol and n-octanol produced is maximized and the amount of n-hexanol produced is minimized.